The present invention relates to mixtures of coal in oil or in other liquid hydrocarbon carriers, which mixtures have controlled sedimentation properties and a sufficiently low viscosity that they can be transported over long distances in conventional oil pipelines and then easily separated into their constituent solid and liquid hydrocarbon phases at the desired destination point.
Large reserves of sub-bituminous coal containing relatively high levels of ash-forming minerals and moisture, frequently more than about 9 weight percent of each, are found in western Canada and in the western United States. The cost of cleaning and then transporting such low rank coals by rail to markets in eastern Canada and the midwestern United States can range from two to four times more than the value of the coal at the mine mouth. Since a number of sub-bituminous coal mines are located close to existing multiple product, commercial pipelines which lead to markets in the midwest and eastern portions of Canada and the United States and since pipeline tariffs for long-distance transport can be significantly less than the cost of rail transportation of bulk products, it is reasonable to consider the use of these existing pipelines for transporting coal which has been cleaned at the mine mouth to market in the form of a slurry at a cost which is hopefully lower than that of conventional rail transport. The fact that there are a significant number of coal-burning and coal-capable utility boilers located within a few miles of these existing commercial pipelines both in Canada and in the United States adds to the cost-saving potential of slurry transport via pipelines.
Proposals have been made to transport coals in the form of coal-water slurries and coal-oil slurries. The transport of coal-water slurries poses several disadvantages. It requires the disposal of large quantities of water at the coal's destination which in turn poses environmental and economic liabilities. Furthermore, pipeline tariffs are related to volume of product transported and, since coal normally represents only about one-third of a slurry's volume, approximately two-thirds of the pipeline tariff would be for the transport of water which has no value as a fuel.
Coal-oil slurries, on the other hand, appear to be a more economical and practical way of transporting coals. First, crude oil and other liquid hydrocarbons are currently transported long distances by pipeline across Canada, the United States, and other countries. Thus, if these oils and other liquid hydrocarbons could be used as a carrier for the coal, the cost of transporting the coal would be only for the actual coal volume plus whatever additional surcharge is imposed as a result of the higher viscosity for the slurry compared to the crude oil or other liquid hydrocarbons normally transported through the pipeline. Unfortunately, the transporting of coal-oil slurries or mixtures have posed a number of insurmountable problems. First, during pipeline shutdown, the coal has a tendency to settle through the oil into a relatively hard pack at the bottom of the pipeline. This hard-packed coal sediment is difficult if not impossible to uniformly redisperse when the pipeline is again put into operation. Also, separating the coal from the oil or other liquid hydrocarbon at the destination point has proved to be difficult. The separation is essential if the oil or other liquid hydrocarbon is to be used for its originally intended purpose, e.g., as a feed to an oil refinery. To qualify for such a use, the oil must have a low particulates and water content, properties which have been found difficult to achieve in the past.